1. Field of the Invention
This invention relates to a high performance lubricating oil composition, which allows easy cold plastic working for metal materials only by coating and which is less corrosive to ferrous materials, and a process for producing the same.
2. Discussion of the Related Art
The following lubricating method has been widely used for cold plastic working for steel: This lubricating method forms zinc phosphate coating with zinc stearate and sodium stearate on workpieces. It has been widely employed because the film formed by this method offers good cold plastic working performance. When this method is applied to workpieces to be plastically cold-worked, it shows a good performance in suppressing the seizure between the workpieces and a die. This method is applicable to a case where a workpiece having a complicated shaped should be formed, and a case where a workpiece should be processed in severe cold plastic working conditions.
Other than the above lubricating method, a method has been known in which a commercially available or a known lubricating oil is employed. The lubricating oil comprises a base oil mixed with a sulfur additive, a phosphorus additive or zinc dialkyldithiophosphate (hereinafter abbreviated to ZnDTP). This method does not require the film forming as required for the above lubricating method, in which zInce phosphate coating with zinc stearate and sodium stearate is formed on workpieces before cold plastic working. In this method, it is only necessary to apply the lubricating oil by spraying it to a workpiece before cold plastic working. Accordingly, this method has an advantage overcoming the following problems associated with the above lubricating method, in which a metal soap film is formed on workpieces before cold plastic working: A whole cold plastic working process cannot be automated, sludge and scale should be removed and dumped, and the waste of metallic soap solution should be properly treated.
The lubricating method, in which a metal soap film is formed on a workpieces, requires that the above lubricant film is formed before cold plastic working. The above lubricant film forming process comprises the following steps requiring very tiresiome operations and done in the following order: pickling, washing with water, zinc phosphate coating, washing with water, neutralizing, metallic soap coating and drying. Consequently, the lubricant film process cannot be incorporated into a series of processing line ranging from a material cutting process to a cold plastic working process, and shold be left alone as a separate and independent process. Thus, the lubricant film forming process interrupts the operation between the material cutting process and the cold plastic working process in a cold plastic working line employing this lubricating method. As a result, such a cold plastic process automation cannot be realized, and this is a serious problem in satisfying the following requirement assigned to current manufacturing shops: providing required goods in required quantities at required times. Further, sludge and scale should be removed and dumped because they are produced in the phosphate coating process. Furthermore, the waste of metallic soap solution should be properly treated. Therefore, this lubricating method has drawbacks resulting in increased labor, costs and times.
The other method, in which the lubricating oil comprising a base oil mixed with a sulfur additive, a phosphorus additive or ZnDTP is employed, has a poorer seizure prevention performance in cold plastic working than that of the lubricating method in which a metal soap film is formed on workpieces. Accordingly, this method has a critical drawback, i.e. it is only applicable to cold plastic working in milder conditions. Its poor seizure prevention performance results from the fact that the seizure prevention is done only by the lubricating oil film and the reaction film generated during cold plastic working.